#include <avr/interrupt.h>
#include <LiquidCrystal_I2C.h>

LiquidCrystal_I2C lcd(0x27, 16, 2);

volatile uint16_t adcValue;
volatile uint16_t previousAdcValue;
volatile bool changeFlag=true;

void setup() {
  //start lcd
  lcd.begin(16, 2);
  // Initialize ADC
  // Use AVcc as the reference
  //and A0 pin as ADC input
  ADMUX = 0b00000000;
  // Enable ADC, Enable ADC Interrupt, and set prescaler to 128
  ADCSRA = 0b11001111;   
  sei(); // Enable global interrupts
}

ISR(ADC_vect){
  adcValue = ADC; // Read the ADC value
  if(adcValue!=previousAdcValue)changeFlag=true;
  previousAdcValue=adcValue;
}


int main() {
  init();
  setup();
  while(true) {
    // If conversion is done, process value
    if(changeFlag) {
    lcd.clear();
    lcd.print((adcValue/1023.0)*5.0);
    lcd.print("V");
    changeFlag=false;
    lcd.setCursor(0, 1);
    }
    // Re-enable conversion with interrupts
    ADCSRA|=1<<ADSC;
  }
}